Stem cells are pluripotent cells derived from somatic tissue capable of differentiating into more specialized cells. For example, hematopoietic stem cells can differentiate into many different types of blood cells, including red blood cells, platelets, and leukocytes.
Hematopoietic stem cells are quite abundant and play a role in the continuous lifelong physiological replenishment of blood cells. Stem cells develop into both hematopoietic lineage cells and non-hematopoietic, tissue specific cells. Recently, stem cells have been found to differentiate into a variety of tissue-specific cell types, such as myocytes, hepatocytes, osteocytes, glial cells, and neurons. For example, stem cells have been shown to cross the blood-brain barrier (Willams and Hickey, Curr. Top. Microbiol. Immunol. 202:221-245, 1995) and differentiate into neurons (Mezey, Science 290:1779-82, 2000). Thus, it is possible that stem cells could be used to treat Parkinson's disease (Polli, Haematologica 85:1009-10, 2000), Alzheimer's disease (Mattson, Exp. Gerontol. 35:489-502, 2000), and traumatic brain injury (Magavi, Nature 405: 892-3, 895, 2000). Stem cells also have been shown to differentiate into fibroblast or fibroblast-like cells, and to express collagen (Periera et al., Proc. Natl. Acad. Sci. 95:1142-7, 1998). Thus, it is possible that stem cells can be used to treat osteogenesis imperfecta and bone fractures. Peterson et al. (Science 284:1168-70, 1999) also have shown that liver cells can arise from stem cells. Thus, stem cells may be of use in treating a variety of pathologies of the liver, including, but not limited to cirrhosis. In addition, bone marrow derived stem cells have been demonstrated to migrate to the site of a myocardial infarction and form myocardium (Orlic, Nature 410:701-5, 2000). Thus, stem cells may be use in treating myocardial infarction.
Since stem cells are capable of differentiating into a broad variety of cell types, they play an important role in the healing and regenerative processes of various tissues and organs. See Koc, O. N., and Lazarus, H. M., Bone Marrow Transplant, 27(3):235-39 (2001). Bone marrow stem cells, including marrow stromal cells (MSCs), injected into a recipient's circulatory system can integrate into various organs and tissues to become mature, terminally differentiated cells. Therefore, activation and enhancement of stem cell trafficking can amplify these physiological processes and provide a potential therapy for various pathologies.